A well-known phenomenon associated with watercraft of all sizes is that the movement of the hull of the craft through the water results in resistance and drag, since the water must be pushed aside as the boat moves forward. The effect is to increase the energy necessary to push the craft forward through the water, the effect becoming greater as the ship increases in size. The “wetted area” of a ship (the portion of the hull that is below the water line) is a factor in the drag caused by the ship, and thus ships having a larger wetted area produce more drag. Furthermore, traditional hull designs with a pointed bow cause a wave to form immediately adjacent the bow as the ship moves through the water, which also increases resistance since the ship must proceed through the wave it has created. This effect is also increased with larger ships. All of these factors together cause a significant decrease in the efficiency of a ship's engines, as resistance and drag must be overcome in order to push the ship forward, the loss of efficiency being greatest with the largest ships.
One well-known approach to reduce the resistance of a large ship passing through the water is the “bulbous bow” hull design. This design incorporates a protruding bulb at the bow of the ship, typically just below the waterline. The bulb forces water to flow up over the bulb as the ship moves through the water. The bulbous bow is designed so that the trough of water flowing off the bulb partially cancels out the bow wave caused by the ship, thereby reducing the ship's wake, and thus reducing the ship hull's resistance as it moves through the water. Although producing this additional wave causes an energy loss, the energy loss is more than compensated for by the reduction in drag caused by damping the wave formed by the bow as it passes through the water. The bulbous bow design is of most benefit to the largest ships traveling at high speeds, since these ships experience the most drag due to the presence of the bow wave. Smaller ships may not benefit, since the increase in wetted area—and thus increased resistance—may be greater than the reduction in drag caused by the reduction of the bow wave.
It may be seen that even when a bulbous bow is employed there remains a large loss of energy as a ship moves through the water, due to the effects described above. The inventor hereof has recognized that it would be desirable to recapture some of this energy in order to provide power to a ship, whether to provide on-board electricity, to augment propulsion, or both. One attempt to capture this lost energy is described in U.S. Pat. No. 8,075,354 to Packard. This patent teaches a marine vessel with a submerged front rotor/turbine that purportedly shields the vessel hull from some of the resistance force of the water, while extracting hydrodynamic energy from displaced water that results from the vessel's motion through the water. It is the inventor's belief, however, that this apparatus would be impractical, since the rotor/turbine extends forward of the bow of the ship, where it would be easily damaged by ice, tugboats, docks, or other solid objects that the ship may contact during normal operation. Repair and maintenance for this device would require underwater work or, more likely, dry docking for the ship, which is very expensive. In light of these clear disadvantages, a practical system that effectively captures some of the energy lost due to a ship's movement through the water to either power electrical devices on the ship or augment propulsion, or both, would be highly desirable. A system such as this that is particularly suited for use with a bulbous bow would be of particular desirability, since ships with a bulbous bow tend to be among the largest, fastest ships and are often used for trans-ocean voyages, and thus such ships would reap the greatest gain by capturing a part of this energy loss.
References mentioned in this background section are not admitted to be prior art with respect to the present invention.